Plasma lamp with dielectric waveguide

ABSTRACT

A dielectric waveguide integrated plasma lamp (DWIPL) with a body consisting essentially of at least one dielectric material having a dielectric constant greater than approximately 2, and having a shape and dimensions such that the body resonates in at least one resonant mode when microwave energy of an appropriate frequency is coupled into the body. A bulb positioned in at least one lamp chamber in the body contains a gas-fill which when receiving energy from the resonating body forms a light-emitting plasma.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.09/809,718 (“'718”) filed on Mar. 15, 2001, entitled “Plasma Lamp WithDielectric Waveguide,” which claims priority to U.S. provisionalapplication Ser. No. 60/222,028 filed on Jul. 31, 2000, entitled “PlasmaLamp.” application Ser. Nos. 09/809,718 and 60/222,028 are herebyincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The field of the present invention relates to devices and methods forgenerating light, and more particularly to electrodeless plasma lamps.

2. Related Art

Electrodeless plasma lamps provide point-like, bright, white lightsources. Because they do not use electrodes, electrodeless plasma lampsoften have longer useful lifetimes than other lamps. Electrodelessplasma lamps in the related art have certain common features. Forexample in U.S. Pat. No. 4,954,755 to Lynch et al., U.S. Pat. No.4,975,625 to Lynch et al., U.S. Pat. No. 4,978,891 to Ury et al., U.S.Pat. No. 5,021,704 to Walter et al., U.S. Pat. No. 5,448,135 to Simpson,U.S. Pat. No. 5,594,303 to Simpson, U.S. Pat. No. 5,841,242 to Simpsonet al., U.S. Pat. No. 5,910,710 to Simpson, and U.S. Pat. No. 6,031,333to Simpson, the plasma lamps direct microwave energy into an air cavity,with the air cavity enclosing a bulb containing a mixture of substancesthat can ignite, form a plasma, and emit light.

The plasma lamps described in these references are intended to providebrighter light sources with longer life and more stable spectra thanelectrode lamps. However, for many applications, light sources that arebrighter, smaller, less expensive, more reliable, and have long usefullifetimes are desired, but such light sources until now have beenunavailable. Such applications include, for example, streetlights andemergency response vehicles. A need exists, therefore, for a verybright, durable light source at low cost.

In the related art, the air-filled cavity of an electrodeless plasmalamp typically is constructed in part by a metal mesh. Metal mesh isused because it contains the microwave energy within the cavity while atthe same time permitting the maximum amount of visible light to escape.The microwave energy is typically generated by a magnetron or solidstate electronics and is guided into the cavity through one or morewaveguides. Once in the air-filled cavity, microwave energy of selectfrequencies resonates, where the actual frequencies that resonate dependupon the shape and size of the cavity. Although there is tolerance inthe frequencies that may be used to power the lamps, in practice, thepower sources are limited to microwave frequencies in the range of 1-10GHz.

Because of the need to establish a resonance condition in the air-filledcavity, the cavity generally may not be smaller than one-half thewavelength of the microwave energy used to power the lamp. Theair-filled cavity and thereby, the plasma lamp itself has a lower limiton its size. However, for many applications, such as for high-resolutionmonitors, bright lamps, and projection TVs, these sizes remainprohibitively large. A need exists therefore for a plasma lamp that isnot constrained to the minimum cavity sizes of the related art.

In the related art, a bulb typically is positioned at a point in thecavity where the electric field created by the microwave energy is at amaximum. The support structure for a bulb preferably is of a size andcomposition that does not interfere with the resonating microwaves, asany interference with the microwaves reduces the efficiency of the lamp.The bulbs, therefore, typically are made from quartz. Quartz bulbs,however, are prone to failure because the plasma temperature can beseveral thousand degrees centigrade, which can bring the quartz walltemperature to near 1000° C. Furthermore, quartz bulbs are unstable interms of mechanical stability and optical and electrical properties overlong periods. A need exists, therefore, for a light source thatovercomes the above-described issues, but that is also stable in itsspectral characteristics over long periods.

In plasma lamps of the related art, the bulb typically contains a noblegas combined with a light emitter, a second element or compound whichtypically comprises sulfur, selenium, a compound containing sulfur orselenium, or any one of a number of metal halides. Exposing the contentsof the bulb to microwave energy of high intensity causes the noble gasto become a plasma. The free electrons within the plasma excite thelight emitter within the bulb. When the light emitter returns to a lowerelectron state, radiation is emitted. The spectrum of light emitteddepends upon the characteristics of the light emitter within the bulb.Typically, the light emitter is chosen to cause emission of visiblelight.

Plasma lamps of the type described above frequently require highintensity microwaves to initially ignite the noble gas into plasma.However, over half of the energy used to generate and maintain theplasma typically is lost as heat, making heat dissipation a problem. Hotspots can form on the bulb causing spotting on the bulb and therebyreducing the efficiency of the lamp. Methods have been proposed toreduce the hot spots by rotating the lamp to better distribute theplasma within the lamp and by blowing constant streams of air at thelamp. These solutions, however, add structure to the lamp, therebyincreasing size and cost. Therefore, a need exists for a plasma lampthat requires less energy to ignite and maintain the plasma, andincludes a minimum amount of additional structure for efficientdissipation of heat.

BRIEF SUMMARY OF THE INVENTION

This invention provides distinct advantages over the electrodelessplasma lamps in the related art, such as brighter and spectrally morestable light, greater energy efficiency, smaller overall lamp sizes, andlonger useful life spans. Rather than using a waveguide with anair-filled resonant cavity, embodiments of the invention use a waveguidehaving a body consisting essentially of at least one dielectric materialhaving a dielectric constant greater than approximately 2. Suchdielectric materials include solid materials such as ceramics, andliquid materials such as silicone oil. A larger dielectric constantpermits “dielectric waveguides” to be significantly smaller thanwaveguides of the related art, enabling their use in many applicationswhere the smallest size achievable heretofore has made such useimpossible or impractical.

In one aspect of the invention, a lamp includes a waveguide having abody comprising at least one dielectric material and having at least onesurface determined by a waveguide outer surface. Each material has adielectric constant greater than approximately 2. The lamp furtherincludes a first microwave probe positioned within and in intimatecontact with the body, adapted to couple microwave energy into the bodyfrom a microwave source having an output and an input and operatingwithin a frequency range from about 0.5 to about 30 GHz at a preselectedfrequency and intensity. The probe is connected to the source output.The frequency and intensity and the body shape and dimensions areselected so that the body resonates in at least one resonant mode havingat least one electric field maximum. The lamp further includes at leastone lamp chamber depending, respectively, from at least one waveguideouter surface into the body, with each chamber at a locationcorresponding to an electric field maximum during operation. The lampfurther includes a gas-fill in each chamber which when receivingmicrowave energy from the resonating body forms a light-emitting plasma.

In another aspect of the invention, a lamp includes a waveguide having abody with a main portion including a solid dielectric material and abody first side, and a protrusion extending from the first side andterminating in a second side determined by a waveguide outer surfacefrom which depends a lamp chamber into the protrusion. The lamp furtherincludes a microwave probe positioned within and in intimate contactwith the body main portion, adapted to couple microwave energy into themain portion from a microwave source having an output and an input andoperating within a frequency range from about 0.5 to about 30 GHz at apreselected frequency and intensity. The probe is connected to thesource output. The frequency and intensity and the body main portionshape and dimensions are selected such that the main portion resonatesin at least one resonant mode having at least one electric fieldmaximum. The lamp further includes a bulb envelope substantially withinthe chamber, containing a gas-fill which when receiving microwave energyfrom the resonating body main portion forms a light-emitting plasma.

In still another aspect of the invention, a lamp includes a waveguidehaving a body including a solid dielectric material and a sidedetermined by a waveguide outer surface from which depends a lampchamber. The chamber aperture is circumscribed by a bulb envelopesupport sealed to the outer surface. The lamp further includes amicrowave probe positioned within and in intimate contact with the body,adapted to couple microwave energy into the body from a microwave sourcehaving an output and an input and operating within a frequency rangefrom about 0.5 to about 30 GHz at a preselected frequency and intensity.The probe is connected to the source output. The frequency and intensityand the body shape and dimensions are selected such that the bodyresonates in at least one resonant mode having at least one electricfield maximum. The lamp further includes a bulb envelope substantiallywithin the chamber and hermetically sealed to the bulb envelope support.The bulb envelope contains a gas-fill which when receiving microwaveenergy from the resonating body main portion forms a light-emittingplasma.

In yet another aspect of the invention, a method for producing lightincludes the step of coupling microwave energy into a waveguide having abody including at least one dielectric material and having at least onesurface determined by a waveguide outer surface from which depends atleast one lamp chamber into the body. Each material has a dielectricconstant greater than approximately 2. The energy frequency andintensity and the body shape and dimensions are selected such that thebody resonates in a least one resonant mode having at least one electricfield maximum. The method further includes the step of directingresonant microwave energy into the lamp chamber(s), with each lampchamber containing a gas-fill including a plasma-forming gas and a lightemitter. The method further includes the step of creating a plasma byinteracting the resonant energy with the gas-fill, thereby causingemission of light.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a sectional view of a dielectric waveguide integratedplasma lamp (DWIPL) including a waveguide having a body consistingessentially of a solid dielectric material, integrated with a bulbenvelope containing a light-emitting plasma.

FIGS. 2A and 2B illustrate sectional views of alternative embodiments ofa DWIPL.

FIGS. 3A and 3B illustrate a sectional view of an alternative embodimentof a DWIPL wherein the bulb envelope is thermally isolated from thedielectric waveguide.

FIGS. 4A-D illustrate different resonant modes within a rectangularprism-shaped dielectric waveguide.

FIGS. 5A-C illustrate different resonant modes within a cylindricalprism-shaped dielectric waveguide.

FIG. 6 illustrates a DWIPL embodiment wherein a feedback mechanismprovides information to a microwave source from a probe probing thewaveguide field, thereby dynamically maintaining a resonant mode withinthe waveguide.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to the drawings, FIG. 1 illustrates a preferred embodimentof a dielectric waveguide integrated plasma lamp (DWIPL) 101. DWIPL 101includes a source 115 of microwave radiation, a waveguide 103 having abody 104 formed of a solid dielectric material, and a microwave probe117 coupling the radiation source 115 to the waveguide 103. Waveguide103 is determined by opposed sides 103A, 103B, and opposed sides 103C,103D generally transverse to sides 103A, 103B. As used herein, the term“waveguide” generally refers to any device having a characteristic andpurpose of at least partially confining electromagnetic energy. As usedherein, the term “dielectric waveguide” refers to a waveguide having abody consisting essentially of at least one dielectric material having adielectric constant greater than approximately 2. As used herein, theterm “probe” is synonymous with “feed” in the '718 application. DWIPL101 further includes a bulb 107, disposed proximate to side 103A andpreferably generally opposed to probe 117, containing a gas-fill 108including a noble gas and a light emitter, which when receivingmicrowave energy at a predetermined operating frequency and intensityforms a plasma and emits light. As used herein, the term “ignition”means initial breakdown of atoms or molecules of the initially neutralgas-fill into ions. As used herein, the term “bulb” refers to anenclosure disposed substantially if not totally within a lamp chamber ina waveguide body, which either is a “bulb envelope,” viz., an enclosuredetermined by a surrounding wall and a window covering the chamberaperture and hermetically sealed to the wall, or is a self-encloseddiscrete bulb within the chamber. The term “bulb cavity,” where usedherein, refers to the combination of a lamp chamber and a discrete bulbdisposed within the chamber. Because the gas-fill is confined to adiscrete bulb, a bulb cavity need not be hermetically sealed.

Source 115 provides microwave energy to waveguide 103 via probe 117. Thewaveguide contains and guides the energy to an enclosed lamp chamber105, depending from side 103A into body 104, in which is disposed bulb107. This energy frees electrons from noble gas atoms, thereby creatinga plasma. The free electrons excite the light emitter. De-excitation ofthe light emitter results in emission of light. As will become apparent,the DWIPL embodiments disclosed herein offer distinct advantages overthe plasma lamps in the related art, such as an ability to producebrighter and spectrally more stable light, greater energy efficiency,smaller overall lamp sizes, and longer useful life spans.

The microwave source 115 in FIG. 1 is shown schematically as solid stateelectronics; however other devices commonly known in the art operatingin the 0.5-30 GHz range may also be used, including but not limited toklystrons and magnetrons. The preferred operating frequency range forsource 115 is from about 500 MHz to about 10 GHz.

Depending upon the heat sensitivity of source 115, the source may bethermally isolated from bulb 107, which during operation typicallyreaches temperatures between about 700° C. and about 1000° C. Thermalisolation of bulb 107 from source 115 provides a benefit of avoidingdegradation of the source due to heating. Additional thermal isolationof the source may be accomplished by any one of a number of methodscommonly known in the art, including but not limited to using aninsulating material or vacuum gap occupying an optional space 116between the source 115 and waveguide 103. If the space 116 is included,appropriate microwave probes are used to couple the source 115 to thewaveguide 103.

In FIG. 1, probe 117 that transports microwave energy from the source115 to the waveguide 103 preferably is a coaxial probe. However, any oneof several different types of microwave probes known in the art may beused, such as microstrip lines or fin line structures.

Due to mechanical and other considerations such as heat, vibration,aging and shock, when feeding microwave energy into the dielectricmaterial, contact between the probe 117 and waveguide 103 preferably ismaintained using a positive contact mechanism 121. The mechanismprovides a constant pressure by the probe on the waveguide to minimizethe possibility that microwave energy will be reflected back through theprobe rather than entering the waveguide. In providing constantpressure, the contact mechanism compensates for small dimensionalchanges in the probe and waveguide that may occur due to thermal heatingor mechanical shock. Contact mechanism 121 may be a spring loadeddevice, such as illustrated in FIG. 1, a bellows type device, or anyother device commonly known in the art that can sustain a constantpressure for continuously and steadily transferring microwave energy.

When coupling probe 117 to waveguide 103, intimate contact preferably ismade by depositing a metallic material 123 directly on the waveguide atits point of contact with the probe. This material eliminates gaps thatmay disturb the coupling, and preferably includes gold, silver orplatinum, although other conductive materials may be used. The materialmay be deposited using any one of several methods commonly known in theart, such as depositing the material as a liquid and then firing it inan oven to provide a solid contact.

In FIG. 1, waveguide 103 is in the shape of a rectangular prism.However, the waveguide may have a cylindrical prism shape, a sphere-likeshape, or any other shape that can efficiently guide microwave energyfrom the probe 117 to the bulb 107, including a complex, irregular shapewhose resonant frequencies preferably are determined usingelectromagnetic theory simulation tools. The actual dimensions of thewaveguide will vary depending upon the microwave operating frequency andthe dielectric constant of the waveguide body 104.

In one preferred embodiment, body 104 has a volume of approximately12,500 mm³ and a dielectric constant of approximately 9, and theoperating frequency is approximately 2.4 GHz. Waveguide bodies of thisscale are significantly smaller than the waveguides in the plasma lampsof the related art. Thus, waveguides according to the present inventionrepresent a significant advance over the related art because theirsmaller size allows them to be used in many applications where thesmallest size achievable heretofore has precluded or made whollyimpractical such use. By using materials with larger dielectricconstants, even smaller sizes can be achieved. Besides the obviousadvantages provided by smaller size, size reduction translates intohigher power density and lower loss, thereby making lamp ignitioneasier.

Regardless of its shape and size, waveguide body 104 preferably includesa solid dielectric material having the following properties: (1) adielectric constant greater than approximately 2; (2) a loss tangentless than approximately 0.01; (3) a thermal shock resistance quantifiedby a failure temperature greater than approximately 200° C.; (4) a DCbreakdown threshold greater than approximately 200 kilovolts/inch; (5) acoefficient of thermal expansion less than approximately 10⁻⁵/° C.; (6)a zero or slightly negative temperature coefficient of the dielectricconstant; (7) stoichiometric stability over a temperature range of about−80° C. to about 1000° C.; and (8) a thermal conductivity ofapproximately 2 W/mK (watts per milliKelvin).

Certain ceramics, including alumina, zirconia, titanates and variationsor combinations of these materials may satisfy many of the abovepreferences, and may be used because of their electrical andthermo-mechanical properties. Alternatively, the dielectric material maybe a silicone oil. Preferably, body 104 has a substantial thermal masswhich aids efficient distribution and dissipation of heat and providesthermal isolation between source 115 and bulb 107.

Referring to FIG. 2A, a DWIPL 200 includes a waveguide 203 having a body204 consisting essentially of a solid dielectric material, and a side203A with an enclosed lamp chamber 205 depending from side 203A intobody 204. A bulb 207 is disposed within the chamber. DWIPL 200 furtherincludes a microwave probe 209 generally opposed to chamber 205.Preferably, bulb 207 is in the same plane as probe 209, where theelectric field of the microwave energy is at a maximum. Where more thanone maximum of the electric field is present in waveguide 203, thechamber and bulb are positioned at one maximum and the probe at anothermaximum. By placing the probe and bulb at field maxima, the amount ofenergy transferred into the bulb is maximized.

Referring to FIG. 2B, a DWIPL 220 includes a waveguide 223 having a body224 with a main portion 224A consisting essentially of a soliddielectric material. Body 224 further includes a convexly-shaped portion224B which protrudes outwardly from portion 224A to form an enclosedlamp chamber 225. As in DWIPL 200, a bulb 227 disposed within chamber225 is positioned generally opposed to a microwave probe 221. Incontrast to DWIPL 200, bulb 227 may be positioned in a plane other thanthe plane of probe 221 where more than one maximum of the electric fieldis present in waveguide 223.

Returning to FIG. 1, sides 103A, 103B, 103C, 103D of waveguide 103, withthe exception of those surfaces depending from side 103A into body 104which form lamp chamber 105, are coated with a thin metallic coating 119which reflects microwaves in the operating frequency range. The overallreflectivity of the coating determines the level of energy within thewaveguide. The more energy that can be stored within the waveguide, thegreater the efficiency of lamp 101. Preferably, coating 119 alsosuppresses evanescent radiation leakage and significantly attenuates anystray microwave field(s).

Microwave leakage from chamber 105 is significantly attenuated bychoosing the chamber dimensions to be significantly smaller than thewavelength(s) of the microwaves used to operate lamp 101. For example,the length of the diagonal of a window sealing the chamber should beconsiderably less than half the microwave wavelength (in free space).

Still referring to FIG. 1, bulb 107 includes an outer wall 109 having aninner surface 110, and a window 111. Alternatively, the lamp chamberwall acts as the outer wall of the bulb. The components of bulb 107preferably include at least one dielectric material, such as a ceramicor sapphire. In one embodiment, the ceramic in the bulb is the same asthe material used in body 104. Dielectric materials are preferred forthe bulb 107 because the bulb preferably is surrounded by the body 104,and the dielectric materials facilitate efficient coupling of microwaveenergy with the gas-fill 108 in the bulb.

In FIG. 1, outer wall 109 is coupled to window 111 using a seal 113,thereby determining a bulb envelope 127 which contains the gas-fill 108.The plasma-forming gas preferably is a noble gas. The light emitterpreferably is a vapor formed of any one of a number of elements orcompounds known in the art, such as sulfur, selenium, a compoundcontaining sulfur or selenium, or a metal halide such as indium bromide(InBr).

To confine the gas-fill within the bulb envelope, the seal 113preferably is a hermetic seal. Outer wall 109 preferably includesalumina because of its white color, temperature stability, low porosity,and coefficient of thermal expansion. However, other materials thatprovide one or more of these properties may be used. Preferably, outerwall 109 is contoured to maximize the amount of light reflected out ofchamber 105 through window 111. For instance, the outer wall may have aparabolic contour. However, other outer wall contours or configurationsthat facilitate directing light out through the window may be used.

Window 111 preferably includes sapphire for high light transmissivityand because its coefficient of thermal expansion matches well with thatof alumina. Alternatively, other materials having similar lighttransmittance and thermal expansion properties may be used.Alternatively, window 111 includes a lens to collect the emitted light.

As referenced above, during operation bulb 107 may reach temperatures ofup to about 1000° C. Under such conditions, body 104 acts as a heat sinkfor the bulb. By reducing the heat load and heat-induced stress on thevarious elements of DWIPL 101, the lamp's useful life span can beincreased beyond the life span of electrodeless lamps in the relatedart. As shown in FIG. 1, effective heat dissipation may be obtained byattaching a plurality of heat-sinking fins 125 to sides 103A, 103C and103D. In DWIPL 220 (see FIG. 2B), lamp chamber 225 extends away from themain portion 224A of body 224, allowing heat to be removed efficientlyby placing a plurality of fins 222 proximate to bulb 227.

Alternatively, waveguide body 104 includes a dielectric, such as atitanate, which generally is unstable at high temperature. In suchembodiments, the waveguide 103 preferably is shielded from the heatgenerated in bulb 107 by interposing a thermal barrier between the bodyand bulb. Alternatively, the outer wall 109 includes a material with lowthermal conductivity, such as an NZP (NaZr₂(PO₄)₃) ceramic, which actsas a thermal barrier.

FIGS. 3A and 3B illustrate a DWIPL 300 wherein a vacuum gap acts as athermal barrier. As shown in FIG. 3A, DWIPL 300 includes a bulb envelope313 disposed within a lamp chamber 315 which is separated from body 312of a waveguide 311 by a vacuum gap 317 whose thickness is dependent uponmicrowave propagation characteristics and the material strengths ofwaveguide body 312 and bulb envelope 313. The vacuum minimizes heattransfer between the bulb and waveguide.

FIG. 3B illustrates a magnified view of bulb envelope 313, chamber 315and vacuum gap 317. The boundaries of gap 317 are formed by thewaveguide 311, a bulb envelope support 319, and bulb envelope 313.Support 319 is sealed to the waveguide and extends over the edges ofchamber 315. The support includes a material having high thermalconductivity, such as alumina, to help dissipate heat from the bulb.

Embedded in support 319 is an access seal 321 which maintains a vacuumwithin gap 317 when bulb envelope 313 is in place. Preferably, the bulbenvelope 313 is supported by and hermetically sealed to support 319.Once a vacuum is established in gap 317, heat transfer between the bulbenvelope and waveguide is substantially reduced.

Preferably, DWIPLs 101, 200, 220 and 300 operate at a microwavefrequency in the range of about 0.5 to 10 GHz. The operating frequencyis preselected so as to excite one or more 15 resonant modes supportedby the size and shape of the waveguide, thereby establishing one or moreelectric field maxima within the waveguide. When used as a resonantcavity, at least one dimension of the waveguide is preferably an integernumber of half-wavelengths.

FIGS. 4A, 4B and 4C schematically illustrate three DWIPLs 410, 420, 430,each operating in a different resonant mode. It is to be understood thateach of these figures represents DWIPL 101, DWIPL 200, DWIPL 220 orDWIPL 300 operating in the respective resonant mode depicted. Referringto FIG. 4A, DWIPL 410 operates in a first resonant mode 411 where thelength of one axis of a rectangular prism-shaped waveguide 417 isone-half the wavelength of the microwave energy used. In FIG. 4B, DWIPL420 operates in a second resonant mode 421 where the length of one axisof a rectangular prism-shaped waveguide 427 equals the microwavewavelength. In FIG. 4C, DWIPL 430 operates in a third resonant mode 431where the length of one axis of a rectangular prism-shaped waveguide 437is three-halves the microwave wavelength. DWIPL 430 includes first andsecond microwave probes 433, 434 which supply energy to the waveguide.The probes may be coupled to a single microwave source or individuallyto separate sources. DWIPLs 410, 420, 430 further include, respectively,a bulb cavity 415, 425, 435.

In DWIPLs 410, 420, 430, bulb cavities 415, 425, 435, respectively, andprobes 413, 423, and (433, 434), respectively, are preferably positionedwith respect to waveguides 417, 427, 437, respectively, at locationswhere the electric fields are at an operational maximum. However, thebulb cavity and probe(s) do not necessarily have to lie in the sameplane.

FIG. 4D schematically illustrates a DWIPL 440 wherein a single microwaveprobe 443 provides energy to a waveguide 447 having first and secondbulb cavities 445, 446, each positioned with respect to the waveguide atlocations where the electric field is at a maximum. It is to beunderstood that FIG. 4D represents DWIPL 101, DWIPL 200, DWIPL 220 orDWIPL 300 operating in the resonant mode depicted, but with the DWIPLmodified to include two bulb cavities.

FIGS. 5A, 5B and 5C schematically illustrate three DWIPLs 510, 520, 530each having a cylindrical prism-shaped waveguide 517, 527, 537,respectively, and operating in a different resonant mode. It is to beunderstood that each of these figures represents DWIPL 101, DWIPL 200,DWIPL 220 or DWIPL 300 operating in the respective resonant modedepicted, but with the DWIPL modified to have a cylindrical waveguide.In each DWIPL, the height of the cylinder is less than its diameter, andthe diameter is close to an integer multiple of the lowest orderhalf-wavelength that can resonate within the waveguide. Placing thesedimensional constraints on the cylinder results in the lowest resonantmode being independent of cylinder height so that the cylinder diameterdictates the fundamental mode of the energy within the waveguide.Cylinder height can thus be optimized for other requirements such assize and heat dissipation. In FIG. 5A, a microwave probe 513 ispositioned directly opposed to bulb cavity 515 where the zeroeth orderBessel mode 511 is a maximum. In FIG. 5B, cylindrical waveguide 527 hasa diameter close to one wavelength long, so that the first order Besselmode 521 is excited. Probe 523 is positioned at the field maximum and isdiagonally opposed to bulb cavity 525. In FIG. 5C, cylindrical waveguide537 has a diameter close to three half-wavelengths long so that thereare two electric field maxima at which are positioned probes 533, 534which provide energy to the waveguide. Bulb cavity 535 is disposedsymmetrically between the two probes. Generally, in a DWIPL having acylinder-shaped waveguide the bulb cavity and probe(s) are preferablypositioned with respect to the waveguide at locations where the electricfield is a maximum.

A dielectric waveguide provides several distinct advantages. Firstly, asdiscussed above, the waveguide body can be used to dissipate heatgenerated in the bulb. Secondly, higher power densities can be achievedwithin a dielectric waveguide than are possible in plasma lamps with aircavities such as those in present use. Depending on the dielectricconstant of the material used for the waveguide body, the energy densityof a dielectric waveguide will be somewhat or substantially greater thanthe energy density in an air cavity waveguide of similiar dimensions ina plasma lamp of the related art.

Referring again to FIG. 1, high resonant energy within waveguide 103 ofDWIPL 101, corresponding to a high Q-value in the waveguide (where Q isthe ratio of the operating frequency to the frequency width of theresonance), results in high evanescent leakage of microwave energy intochamber 105. High leakage into the chamber leads to quasi-staticbreakdown of the noble gas within envelope 127, thereby generating thefirst free electrons. The oscillating energy of the free electronsscales as Iλ², where I is the circulating intensity of the microwaveenergy and λ is the wavelength. Thus, the higher the microwave energy,the greater is the oscillating energy of the free electrons. By makingthe oscillating energy greater than the ionization potential of the gas,electron-neutral collisions result in efficient build-up of plasmadensity.

Once a plasma is formed in DWIPL 101 and the incoming power is absorbed,the waveguide's Q-value drops due to the conductivity and absorptionproperties of the plasma. The drop in Q-value is generally due to achange in the impedance of the waveguide. After plasma formation, thepresence of the plasma in the chamber makes the chamber absorptive tothe resonant energy, thus changing the waveguide impedance. This changein impedance is effectively a reduction in the overall reflectivity ofthe waveguide. By matching the reflectivity of the probe to be close tothe reduced reflectivity of the waveguide, a relatively low netreflection back into the energy source is realized.

Much of the energy absorbed by the plasma eventually appears as heatsuch that the bulb temperature may approach 1000° C. When the waveguideis also used as a heat sink, as previously described, the dimensions ofthe waveguide may change due to thermal expansion. If the waveguideexpands, the microwave frequency that will resonate within the waveguidechanges and resonance is lost. In order for resonance to be maintained,the waveguide must have at least one dimension equal to an integermultiple of the half-wavelength of the microwaves being generated bysource 115.

A DWIPL embodiment that compensates for such dimensional changesincludes a waveguide having a body consisting essentially of a soliddielectric material with a temperature coefficient for its refractiveindex that is approximately equal and opposite in sign to itscoefficient of thermal expansion. Dimensional changes due to thermalheating are offset by a change in refractive index, thus decreasing thepossibility that resonance will be interrupted. Such materials includetitanates. Alternatively, dimensional changes due to heating may becompensated for by tapering the walls of the waveguide.

FIG. 6 schematically shows a DWIPL 610 operated in a dielectric resonantoscillator mode wherein first and second microwave probes 613, 615 arecoupled between a dielectric waveguide 611, which may be of any shapepreviously discussed, and a microwave energy source 617. Source 617 ispreferably broadband with a high gain and high output power, and iscapable of driving the plasma to emission. DWIPL 610 further includes abulb cavity 619.

Probe 613 generally operates as described for the other embodimentsdisclosed herein. Probe 615 probes the waveguide 611 to instantaneouslysample the field (including amplitude and phase information containedtherein), and provides the sampled field information via a feedbackmeans 612 to an input 617A of energy source 617 or to a separateamplifier. In probing the waveguide, probe 615 also preferably acts tofilter out stray frequencies, leaving only the resonant frequency withinthe waveguide. Preferably, probes 613, 615 and bulb cavity 619 are eachpositioned with respect to waveguide 611 at locations where the electricfield is at a maximum. Using the sampling information provided by probe615, the energy source 617 amplifies the resonant energy within thewaveguide. The source thereby adjusts its output frequency todynamically maintain one or more resonant modes in the waveguide. Thecomplete configuration thus forms a resonant oscillator. In this manner,automatic compensation may be realized for frequency shifts due toplasma formation and changes in waveguide dimensions and dielectricconstant due to thermal effects, enabling continuous operation of thelamp.

The dielectric resonant oscillator mode also enables DWIPL 610 to havean immediate re-strike (i.e., re-ignition) capability after being turnedoff. As previously discussed, the resonant frequency of the waveguidemay change due to thermal expansion and/or changes in the dielectricconstant caused by heat generated during operation. Furthermore, theresonant frequency depends upon the state of the plasma. When DWIPL 610is shut down, the light-emitting plasma extinguishes and heat isdissipated resulting in changes in the resonant frequency of thewaveguide.

However, as indicated above, in the resonant oscillator mode the energysource 617 automatically compensates for changes in the resonantfrequency of the waveguide 611. Therefore, regardless of the startupcharacteristics of the waveguide, and providing that energy source 617has the requisite bandwidth, the energy source will automaticallycompensate to achieve resonance within the waveguide. Thus, the energysource immediately provides power to the DWIPL at the optimumplasma-forming frequency.

While several embodiments for carrying out the invention have been shownand described, it will be apparent to those skilled in the art thatadditional modifications are possible without departing from theinventive concepts detailed herein. It is to be understood, therefore,there is no intention to limit the invention to the particularembodiments disclosed. On the contrary, it is intended that theinvention cover all modifications, equivalences and alternativeconstructions falling within the spirit and scope of the invention asexpressed in the appended claims.

1. A lamp comprising: (a) a waveguide having a body of a preselected shape and dimensions, the body comprising at least one dielectric material and having at least one surface determined by a waveguide outer surface, each said material having a dielectric constant greater than approximately 2; (b) a first microwave probe positioned within and in intimate contact with the body, adapted to couple microwave energy into the body from a microwave source having an output and an input and operating within a frequency range from about 0.5 to about 30 GHz at a preselected frequency and intensity, the probe connected to the source output, said frequency and intensity and said body shape and dimensions selected so that the body resonates in at least one resonant mode having at least one electric field maximum; (c) the body having at least one lamp chamber depending, respectively, from at least one said waveguide outer surface, each chamber at a location corresponding to an electric field maximum during operation; and (d) a gas-fill in each chamber which when receiving microwave energy from the resonating body forms a light-emitting plasma.
 2. The lamp of claim 1 wherein each said dielectric material is a solid material.
 3. The lamp of claim 1 wherein each said dielectric material is a liquid material.
 4. The lamp of claim 1 wherein each said dielectric material is selected from the group consisting of solid materials having a dielectric constant greater than approximately 2, and liquid materials having a dielectric constant greater than approximately
 2. 5. The lamp of claim 2 or 3 or 4, wherein each said dielectric material has a loss tangent less than approximately 0.01.
 6. The lamp of claim 2 or 3 or 4, wherein each said dielectric material has a thermal shock resistance quantified by a failure temperature greater than approximately 200° C.
 7. The lamp of claim 2 or 3 or 4, wherein each said dielectric material has a DC breakdown threshold greater than approximately 200 kilovolts/inch.
 8. The lamp of claim 2 or 3 or 4, wherein each said dielectric material has a coefficient of thermal expansion less than approximately 10⁻⁵/° C.
 9. The lamp of claim 2 or 3 or 4, wherein the dielectric constant of each said dielectric material has a zero or slightly negative temperature coefficient.
 10. The lamp of claim 2 or 3 or 4, wherein each said dielectric material has stoichiometric stability over a temperature range of about −80° C. to about 1000° C.
 11. The lamp of claim 2 or 3 or 4, wherein each said dielectric material has a thermal conductivity of approximately 2 W/mK (watts per milliKelvin).
 12. The lamp of claim 2 or 3 or 4, wherein at least one waveguide outer surface has an outer coating of a metallic material.
 13. The lamp of claim 12 wherein a plurality of heat-sinking fins are attached to at least one said metallic outer coating.
 14. The lamp of claim 2 or 3 or 4, wherein the gas-fill in at least one said lamp chamber is contained within a bulb envelope comprising a surrounding wall hermetically coupled to a window covering the chamber, the window substantially transparent to the light emitted by the plasma.
 15. The lamp of claim 14, wherein at least one bulb envelope comprises at least one dielectric material having a dielectric constant greater than approximately
 2. 16. The lamp of claim 14, wherein at least one said bulb envelope is interior to said lamp chamber.
 17. The lamp of claim 14, wherein a portion of at least one said bulb envelope is exterior to said lamp chamber.
 18. The lamp of claim 16, wherein at least one said window comprises a focusing lens.
 19. The lamp of claim 17, wherein at least one said window comprises a focusing lens.
 20. The lamp of claim 2 or 3 or 4, wherein the gas-fill in at least one said lamp chamber is contained within a self-enclosed discrete bulb disposed therein, the chamber and bulb comprising a bulb cavity, the bulb positioned at an electric field maximum and transparent to the light emitted by the plasma.
 21. The lamp of claim 2 or 3 or 4, wherein the gas-fill in each said lamp chamber comprises a plasma-forming gas and a light emitter.
 22. The lamp of claim 21, wherein the plasma-forming gas is a noble gas.
 23. The lamp of claim 21, wherein the light emitter is selected from the group consisting of sulfur, selenium, compounds containing sulfur, compounds containing selenium, and metal halides.
 24. The lamp of claim 2 or 3 or 4, wherein light emitted by the plasma is selected from the group consisting of ultraviolet light, visible light, and infrared light.
 25. The lamp of claim 2 or 3 or 4, wherein said operating frequency is in a range from about 0.5 GHz to about 10 GHz.
 26. The lamp of claim 2 or 3 or 4, wherein said body shape is a rectangular prism.
 27. The lamp of claim 2 or 3 or 4, wherein said body shape is a cylindrical prism.
 28. The lamp of claim 2 or 3 or 4, wherein said body shape is a sphere.
 29. The lamp of claim 2 or 3 or 4, wherein the first microwave probe and a lamp chamber are positioned proximate to the same electric field maximum.
 30. The lamp of claim 2 or 3 or 4, wherein the body resonates in a mode having at least two electric field maxima, and the first microwave probe and at least one lamp chamber are positioned proximate to different electric field maxima.
 31. The lamp of claim 2 or 3 or 4, wherein said operating frequency and intensity, and said body shape and dimensions are selected so that the body resonates at a high Q-value prior to plasma formation.
 32. The lamp of claim 2 or 3 or 4, wherein the first microwave probe has a reflectivity closely matching the reduced waveguide reflectivity after plasma formation.
 33. The lamp of claim 2 or 3 or 4, further comprising a second microwave probe positioned within the body.
 34. The lamp of claim 33, wherein the first and second microwave probes are each coupled to a separate microwave source.
 35. The lamp of claim 33, wherein the body resonates in a mode having at least three electric field maxima, and the first microwave probe, the second microwave probe, and at least one lamp chamber are each positioned proximate to different maxima.
 36. The lamp of claim 35, wherein: (a) the first microwave probe, the second microwave probe, and at least one lamp chamber are each positioned proximate to an electric field maximum; (b) the second microwave probe is connected to the microwave source input and probes the body to instantaneously sample the amplitude and phase of the electric field therein; (c) the second probe feeds back the sampled amplitude and phase information to the source input; and (d) the source amplifies the resonant energy within the body and dynamically adjusts the operating frequency to maintain at least one resonant mode within the body, thereby operating the lamp in a dielectric resonant oscillator mode.
 37. A lamp comprising: (a) a waveguide having a body with a main portion comprising a solid dielectric material of a preselected shape and preselected dimensions, and a first body side; (b) the body further having a protrusion extending from said first side and terminating in a second side determined by a waveguide outer surface from which depends a lamp chamber into the protrusion; (c) a microwave probe positioned within and in intimate contact with the body main portion, adapted to couple microwave energy into the main portion from a microwave source having an output and an input and operating within a frequency range from about 0.5 to about 30 GHz at a preselected frequency and intensity, the probe connected to the source output, said frequency and intensity and said body main portion shape and dimensions selected such that the main portion resonates in at least one resonant mode having at least one electric field maximum; and (d) a bulb envelope substantially within the cavity, containing a gas-fill which when receiving microwave energy from the resonating body main portion forms a light-emitting plasma.
 38. The lamp of claim 37 wherein the bulb envelope comprises: (a) a window substantially transparent to the light emitted by the plasma; and (b) an outer wall hermetically coupled with the window and shaped to direct light towards the window, said wall having a thermal expansion coefficient approximately equal to the thermal expansion coefficient of the window.
 39. The lamp of claim 38 wherein said solid dielectric material is a ceramic.
 40. A lamp comprising: (a) a waveguide having a body comprising a solid dielectric material of a preselected shape and preselected dimensions, the body having a first side determined by a first waveguide outer surface; (b) the body having a lamp chamber depending from said waveguide outer surface, the chamber having an aperture circumscribed by a bulb envelope support structure sealed to said outer surface; (c) a microwave probe positioned within and in intimate contact with the body, adapted to couple microwave energy into the body from a microwave source having an output and an input and operating within a frequency range from about 0.5 to about 30 GHz at a preselected frequency and intensity, the probe connected to the source output, said frequency and intensity and said body shape and dimensions selected such that the body resonates in at least one resonant mode having at least one electric field maximum; and (d) a self-enclosed bulb substantially within the lamp chamber and hermetically sealed to the bulb support structure and separated from the waveguide body by a gap, the bulb containing a gas-fill which when receiving microwave energy from the resonating body main portion forms a light-emitting plasma.
 41. The lamp of claim 40 wherein the bulb comprises: (a) a window substantially transparent to the light emitted by the plasma; and (b) a surrounding wall hermetically coupled with the window and shaped to direct light towards the window, said wall having a thermal expansion coefficient approximately equal to the thermal expansion coefficient of the window.
 42. The lamp of claim 41 wherein a vacuum is maintained in the cavity.
 43. The lamp of claim 42 wherein said solid dielectric material is a ceramic.
 44. A method for producing light comprising the steps of: (a) coupling microwave energy characterized by a frequency and intensity into a waveguide having a body of a preselected shape and dimensions, the body comprising at least one dielectric material and having at least one surface determined by a waveguide outer surface from which depends at least one lamp chamber into the body, each said material having a dielectric constant greater than approximately 2, said frequency and intensity and said body shape and dimensions selected such that the body resonates in a least one resonant mode having at least one electric field maximum; (b) directing resonant microwave energy into the lamp chamber(s), each lamp chamber containing a gas-fill comprising a plasma-forming gas and a light emitter; and (c) creating a plasma by interacting the resonant energy with the gas-fill, thereby causing emission of light.
 45. The method of claim 44, further comprising the steps of: (a) sampling the amplitude and phase of the electric field within the waveguide body; and (b) adjusting the operating frequency of the microwave source until the sampled electric field is maximized. 